The invention relates to a rotary drive design by means of which a rotary motion of a tool can be transmitted to a workpiece.
Rotary drive designs which contain an at least approximately cylindrical cavity, or a like projection, the shape of which deviates from a circular cylindrical shape, are known in connection with screws.
In a known screw head design (U.S. Pat. No. 3,584,667), the outer periphery of the cylindrical recess or of the cylindrical projection is formed from alternately inwardly and outwardly directed circular arcs which merge tangentially into one another, the inwardly directed circular arcs having double the diameter of the outwardly directed circular arcs.
In further known drive system having a cylindrical cavity, the cross section of the cavity has outwardly directed lobes and flutes arranged between the lobes. The shape of the lobes and flutes is elliptical. A better force transmission is intended to thus be achieved (U.S. Pat. No. 5,207,132).
Owing to the cylindrical basic shape of the drive design both in the screw and on the tool, and owing to the required manufacturing tolerances, there is always a gap between the torque-transmitting surface of the tool and the torque-receiving surface of the workpiece. This gap leads to the tool, during the rotary drive, being subjected to forces running transversely to the rotational axis, which forces can lead to a disparity between the rotational axis of the tool and the rotational axis of the workpiece.